Heretofore, vibration monitoring apparatus of this type is known which is so constructed that a vibration level detected by a vibration detector mounted on a rotary machine or the like is compared with an alarm level for a fixed period according to the rotational frequency of the rotary machine, so that when the vibration level reaches the alarm level, the single-sided amplitude value of the vibration waveform is calculated by a computer, and that when the calculated result exceeds a control criterion, an alarm is provided.
In vibration monitoring apparatus of this type, it is an important factor that the processing of vibration signals detected by a plurality of vibration detectors is performed at high precision and at high speed by a computer system.